Could someone clarify these sentences in HPACK RFC 7541?

When reading HPACK RFC 7541, I am confused on these sentences, in section
4.2:

"This dynamic table size update MUST occur at the beginning of the first
header block following the change to the dynamic table size. In HTTP/2,
this follows a settings acknowledgment (see Section 6.5.3
<https://tools.ietf.org/html/rfc7540#section-6.5.3> of [HTTP2]
<https://httpwg.org/specs/rfc7541.html#HTTP2>)."

I'm not a English native speaker, and I have difficulty in understanding
these two sentences. Could someone kindly elaborate the detailed sequences
on this, like what happens first, what happens later, making it more clear
to understand?

Thank you in advance!

-- 
Best regards,
Jingcheng Zhang
Beijing, P.R.China